JP2005325818A - Operation controller for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation controller for an engine capable of increasing torque by suppressing occurrence of knocking and performing stable combustion by suppressing EGR gas amount to increase thermal efficiency. <P>SOLUTION: In this operation controller for the engine provided with a valve gear capable of changing and controlling at least intake valve opening time (IVO), intake valve closing time (IVC), and exhaust valve closing time (EVC) to operate the engine 1 by SI mode for starting combustion by spark ignition in accordance with operation regions a to i or HCCI mode for starting combustion by premixed compression self-ignition, valve overlap (OL) is controlled in such a way that it is large and its center is positioned in the vicinity of top dead center (TDC) in high load SI mode, and the intake valve closing time IVC is controlled to a position apart in the rear or front of bottom dead center (BDC). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an engine operation control apparatus, and more particularly, to a torque reduction in a spark ignition (SI) mode in a premixed compression self-ignition engine, an EGR more than necessary in a premixed compression autoignition (HCCI) mode. It relates to the one that can avoid the increase and ignition delay.

In a premixed compression self-ignition engine, a normal diesel engine injects and supplies fuel near the compression top dead center, whereas fuel is injected at an early stage into the combustion chamber at least before the compression top dead center. It is an engine of a system that terminates supply. That is, the premixed compression self-ignition engine is configured such that the fuel and air injected early are sufficiently mixed in advance to form a lean mixed state, and this is self-ignited by piston compression. This premixed compression self-ignition engine is attracting attention from the viewpoint of improving fuel consumption and reducing NOx (see, for example, Patent Document 1).
JP 2000-248985 A

  In this type of premixed compression self-ignition engine, in order to easily stabilize combustion in the HCCI mode, the compression ratio of the engine is increased or the EGR gas amount is increased.

  However, if the compression ratio of the engine is increased, there is a problem that knocking is likely to occur in the high load SI mode, and eventually there is a problem that torque can be suppressed due to knocking restrictions. Further, when the EGR gas amount is increased in the HCCI mode, there is a problem that the thermal efficiency of the engine is lowered, or the amount of the air-fuel mixture sucked is decreased due to the rise of the air-fuel mixture temperature, which eventually narrows the HCCI operation region.

  The present invention has been made in view of the above-described conventional situation, and it is possible to increase the torque by suppressing the occurrence of knocking, and it is possible to increase the thermal efficiency by enabling stable combustion while suppressing the amount of EGR gas. It is an object to provide a control device.

The invention according to claim 1 includes a valve system capable of variably controlling at least an intake valve opening timing (IVO), an intake valve closing timing (IVC), and an exhaust valve closing timing (EVC). In an operation control device for an engine that operates in SI mode in which combustion starts by spark ignition or HCCI mode in which combustion starts by premixed compression self-ignition,
In the high load SI mode, the valve overlap (OL) is controlled to be large and the center thereof is positioned near the top dead center (TDC), and the intake valve closing timing is set after the bottom dead center (BDC) or before It is characterized by controlling to a separated position.

  Here, in the present invention, the opening timing and closing timing of each valve mean the ramp end point and ramp start point of the cam lift curve, respectively. The valve overlap means a period in which both the intake valve and the exhaust valve are open.

  In the present invention, the size and center position of the valve overlap are controlled as described above to enhance the scavenging effect, and the intake valve closing position is controlled as described above to increase the effective compression ratio. This is to reduce the temperature of the intake air and avoid an increase in the intake air temperature.

  Specifically, the valve overlap is controlled to a crank angle of 20 to 120 °, more preferably about 20 to 60 °, which is larger than a normal SI engine, and its center is 20 before top dead center. It is controlled so that it is located in the range of ° to 10 ° after top dead center. The intake valve closing timing is controlled to be within a range of 60 to 100 ° after bottom dead center or 20 to 60 ° before bottom dead center.

According to a second aspect of the present invention, in the engine operation control apparatus similar to the first aspect,
In the medium load HCCI mode, the valve overlap is controlled to be small and the center thereof is located away from the top dead center, and the intake valve closing timing is controlled to be located near the bottom dead center. It is said.

  Here, in the present invention, the size and the center position of the valve overlap are controlled as described above in order to perform a large amount of internal EGR by exhaust backflow, and the intake valve closed position is set to the intake mixing as described above. This is to increase the air volume and increase the effective compression ratio to promote the intake air temperature rise.

  Specifically, the size of the valve overlap is about 0 to 20 ° in crank angle, and is controlled to be substantially zero, and its center is located in the range of 20 to 90 ° after top dead center. To be controlled. The intake valve closing timing is controlled so as to be located at 10 to 30 ° after the bottom dead center.

  According to a third aspect of the present invention, in the engine operation control apparatus as in the first aspect, in the low load HCCI mode or the low load SI mode, the valve overlap is negative, and the center thereof is located away from the top dead center. The intake valve closing timing is controlled to be located in the vicinity after bottom dead center.

  Here, in the present invention, the size of the valve overlap and the center position thereof are controlled as described above by reducing the EGR gas amount by delaying the opening of the exhaust valve and delaying the opening of the intake valve, thereby reducing the pump loss. This is because the gas temperature is raised so that the ignition timing is not delayed.

  Specifically, in order to make the valve overlap negative, the negative overlap is controlled to 0 to 60 °, and the center point is controlled to 20 to 90 ° after top dead center. The intake valve closing timing is controlled to 10 to 30 ° after bottom dead center. However, depending on conditions, it may be expanded to 30 ° before bottom dead center and 60 ° after bottom dead center.

According to a fourth aspect of the present invention, there is provided an engine operation control apparatus similar to the first aspect,
In the high load SI mode, the valve overlap (OL) is controlled to be large and the center thereof is positioned near the top dead center (TDC), and the intake valve closing timing is set after the bottom dead center (BDC) or before Control to a separated position,
In the medium load HCCI mode, the valve overlap is controlled to be small and its center is located away from the top dead center, and the intake valve closing timing is controlled to be located near the bottom dead center,
In the low-load HCCI mode or the low-load SI mode, the valve overlap is controlled to be negative and the center thereof is located away from the top dead center, and the intake valve closing timing is located in the vicinity after the bottom dead center. It is characterized by controlling as follows.

  The size, center position, intake valve opening / closing timing, exhaust valve closing timing, etc. of the valve overlap in claim 4 are the same as in claims 1-3.

  According to the first aspect of the present invention, in the high load SI mode, the valve overlap is largely controlled to be, for example, 20 ° or more in crank angle, and the center thereof is set to the vicinity of the top dead center. As a result, the amount of residual gas in the combustion chamber decreases and the mixture temperature decreases. Further, since the intake valve closing timing is separated from the bottom dead center by early closing or late closing, the effective compression ratio is lowered and the compression temperature is lowered. From these points, knocking hardly occurs, and there is no problem that the torque is suppressed due to the restriction of knocking in the high load SI mode. As a result, the engine torque can be increased.

  According to the second aspect of the present invention, in the medium load HCCI mode, the valve overlap is controlled to be small and the center thereof is located away from the top dead center, so that the internal EGR by the exhaust backflow is performed, and the HCCI EGR gas necessary for ignition is introduced. Further, since the intake valve closing timing is controlled to be located in the vicinity after bottom dead center, the effective compression ratio becomes high, and the HCCI operation can be performed with a smaller EGR gas amount than the HCCI engine having the normal compression ratio.

  According to the invention of claim 3, in the low load HCCI mode or the low load SI mode, the valve overlap is controlled to be negative and the center thereof is located away from the top dead center. It is controlled to be located near the bottom dead center.

  In the low load region where the fuel is low and the A / F is lean, the gas temperature is increased by EGR in order to keep the ignition at an appropriate position. However, if this is done, the G / F (G = EGR gas + means fresh air) becomes too lean and the non-burning region increases, resulting in an increase in HC.

  Therefore, in the present invention, the valve overlap is made negative, the exhaust valve closing timing is advanced, the EGR amount is decreased, and the intake valve opening timing is delayed to reduce the fresh air amount by the throttle effect of the intake valve. Furthermore, by delaying the opening timing of the intake valve and creating a negative overlap, a negative pressure is created in the cylinder to increase the pump loss, thereby increasing the gas temperature, so that the ignition timing is not delayed. Yes.

  Further, in order to increase the effective compression ratio, the intake valve closing timing is set near the bottom dead center. However, if there is a margin in the ignition timing, the fresh air amount can be effectively reduced by moving away from the vicinity of the bottom dead center. If the G / F is reduced, spark ignition is possible with a G / F of 20 to 25, and it is possible to connect to an unloaded or idle SI mode.

  According to the fourth aspect of the invention, since the configuration according to the first, second, and third aspects is provided, the same effect as described above can be obtained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIGS. 1-6 is a figure for demonstrating the operation control apparatus of the gasoline engine by one Embodiment of this invention. 1 and 2 are block configuration diagrams of an operation control device for a gasoline engine, FIGS. 3 and 5 are operation region conceptual diagrams conceptually showing an engine operation region, and FIG. 4 is an overlap and opening / closing of intake valves and exhaust valves. FIG. 6 is a diagram schematically showing the time, and FIG. 6 is an overlap selection map.

  In the figure, 1 is a 4-cycle gasoline engine. The engine 1 is set to a compression ratio ε = 12 to 16, and includes an ignition plug 2 for letting an ignition spark fly into the combustion chamber 1a, and a fuel injection valve 3 that directly injects fuel into the combustion chamber 1a. And a variable valve mechanism 4 that variably controls the opening / closing timing of the intake valve and the phase of the exhaust valve disposed in the combustion chamber 1a.

  The intake system 6 of the engine 1 is provided with a Rishorum type supercharger 7 and an intake air cooler (intercooler) 8 for cooling the supercharged intake air and supplying it to the engine 1. A three-way catalyst 9a is interposed in the exhaust system 9. The supercharger 7 is of a type that can arbitrarily control the discharge capacity, and can control the intake air amount per one rotation.

  The engine 1 further includes an engine control system 10 and a supercharging pressure control system 11. The engine control system 10 controls the fuel injection timing and injection period by the fuel injection valve 3, controls the intake and exhaust valve opening / closing timing by the variable valve mechanism 4, and controls the ignition timing by the spark plug 2. Execute. The supercharging pressure control system 11 executes supercharging pressure control by the supercharger 7.

  The engine 1 of the present embodiment has a spark ignition (SI) mode in which fuel is injected and supplied into the combustion chamber 1 a by the fuel injection valve 3 and sparks are blown by the spark plug 2. And a premixed compression self-ignition (HCCI) mode for self-ignition by piston compression. The engine control system 10 operates the engine 1 by appropriately switching to any one of the modes according to the operation region shown in FIG.

  The engine operation region of the present embodiment is conceptually divided as shown in FIG. 3, for example. Specifically, the load on the engine is divided into three parts, a low load, a medium load, and a high load, and the engine rotation speed is divided into three parts, a low speed, a medium speed, and a high speed. The FIG. 5 shows the engine operation region in the engine of the present embodiment more specifically. Needless to say, the engine operating range of the present invention is not limited to the examples shown in FIGS.

  The engine 1 of this embodiment basically combusts in the spark ignition combustion (SI) mode at the time of high rotation and high load (operation regions a, b, c, f, and i in FIG. 3). At low and medium loads (operation regions d, e, g, and h in FIG. 3), combustion is performed in a premixed compression auto-ignition (HCCI) mode. Note that the SI mode may be employed at the time of low rotation and low load (operation region g in FIG. 3).

  In the present embodiment, the size and central position of the valve overlap (OL), the intake valve opening timing (IVO), the closing timing (IVC), and the exhaust valve closing timing (EVC) according to each operation mode. ) Is controlled as detailed below. The opening timing of the exhaust valve changes in parallel with the closing timing. The valve overlap and the opening / closing timing of each valve are controlled by the crank angle.

[At high load (see operation areas a, b, c in FIG. 3 and FIG. 5 (a)) SI mode]
(i) As shown in FIG. 4A, the valve overlap (OL) is controlled to be large and the center thereof is located near the top dead center. Specifically, the OL is set such that the size is controlled to, for example, 50 ° as a crank angle, and the center thereof is located at 10 ° before the top dead center.

  Control of the size and position of the valve overlap is performed based on a map. More specifically, for example, the overlap amount that provides a high scavenging effect is controlled based on an overlap amount selection map (see FIG. 6) obtained in advance using the engine speed and the engine load as a barometer.

(ii) The intake valve closing timing (IVC) is set before or after bottom dead center. Specifically, it is set to 40 ° before the bottom dead center or 80 ° after the bottom dead center.

  The closing timing of the intake valve is also controlled based on the map. However, when knocking is detected, it is moved away from the bottom dead center in cooperation with the ignition retard (each cycle depends on the ignition timing). If a Rishorum compressor is used as a turbocharger, the engine load (torque) does not change because the intake air amount hardly changes even if the intake valve closing timing is changed.

  Fuel is used as intake stroke injection to prevent knocking by utilizing the intake air cooling effect with a uniform mixture. It is also possible to inject fuel into the intake pipe.

  In the high load SI mode, the control as in the above (i) and (ii) is performed for the following reason.

  In order to facilitate combustion in the premixed compression self-ignition (HCCI) mode, it is effective to set the compression ratio high. However, if the compression ratio is increased, the torque is suppressed due to knocking restrictions in the high load SI mode at normal valve timing.

  In contrast, in the present embodiment, the valve overlap is set to be large and the center position is set to be near the top dead center. The intake pressure is set higher than the back pressure by the supercharger 7. Therefore, an effective scavenging action is obtained, the residual gas amount is reduced, and the mixture temperature is lowered. As a result, the occurrence of knocking can be suppressed while increasing the compression ratio. In addition, the supercharging pressure required to obtain the same intake air amount decreases.

  In this embodiment, the closing timing of the intake valve is set to 40 ° before the bottom dead center or 80 ° after the bottom dead center. Thus, since the intake valve is set at a position away from the bottom dead center by early closing or late closing, the effective compression ratio is lowered and the compression temperature is lowered. As a result, knocking is less likely to occur in terms of the compression temperature of the intake air while increasing the compression ratio. However, the supercharging pressure required to obtain the same intake air amount increases.

  In this way, by effectively combining the point where the overlap is increased to 50 ° or more and the point where the intake valve is closed early or late, natural intake (NA) is achieved by supercharging when the compression ratio is 12. ) A torque about 1.5 times that of the engine can be obtained. Further, even if the compression ratio is increased to about 16, a torque equivalent to or higher than that of the NA engine can be obtained. By effectively combining these functions and effects, a torque about 1.5 times NA can be obtained as a supercharged engine when the compression ratio is 12. Even when the compression ratio is increased to 16, a torque equal to or higher than NA can be obtained.

[Medium load (see operation areas d, e, Fig. 5 (b) in Fig. 3) Supercharging and natural intake HCCI mode]
(i) As shown in FIG. 4 (b), the valve overlap is set to be small and controlled so that its center is located away from the top dead center. Specifically, the valve overlap is controlled to, for example, a crank angle of 10 °, and its center is controlled to 60 ° after top dead center.

(ii) The intake valve closing timing (IVC) is set after and near the bottom dead center, specifically, 20 ° after the bottom dead center.

(iii) The compression ratio of the engine of the present embodiment is set to about 12 to 16, and it is necessary to use a variable capacity mechanical supercharger so as to be G / F (G = fresh air + EGR) that does not generate NOx. A quantity of air is supplied.

  In the engine 1 of the present embodiment, the exhaust valve closing timing is map-controlled so as to obtain an EGR amount at which an appropriate ignition timing is obtained, and in this state, the supercharging amount becomes G / F (= 25) that does not generate NOx. Map control of the turbocharger. Further, the combustion state is detected, and the exhaust valve closing timing is F / B controlled so that the appropriate ignition timing is reached. If the exhaust valve closing timing is advanced, the ignition timing is retarded).

  Here, in fuel injection, G / F can be made uniform by injecting fuel into both exhaust backflow and intake air, thereby preventing the generation of NOx in a local rich zone. In this case, the ignition timing can be controlled for each cycle by changing the ratio of the amount of fuel injected during exhaust backflow and the amount of fuel injected during intake. For example, if the injection amount into the exhaust backflow is increased, the ignition timing is advanced. It is also possible to inject and supply fuel into the intake pipe for the amount injected during intake.

  The valve overlap is set as small as 10 ° and the center is set apart from the top dead center, so it is exhausted regardless of the intake pipe pressure, whether it is supercharged or not. A large amount of internal EGR by backflow is performed. When the intake valve is closed, it is set after and near the bottom dead center, so that the amount of intake air-fuel mixture increases and the effective compression ratio becomes high.

  Thus, since the compression ratio is set higher than that of the conventional spark ignition engine and the intake valve closing timing is set near the bottom dead center, the effective compression ratio can be made high, and it is less than the HCCI engine of the normal compression ratio. HCCI operation can be performed with the EGR amount. In this case, it is more effective to increase the intake air temperature by bypassing the intake air cooler 8. In the same G / F, the smaller the EGR, the higher the specific heat ratio, so that the cycle efficiency increases.

  In addition, EGR necessary for self-ignition is introduced by making the exhaust valve close timing after top dead center by flowing backward from the exhaust port. The valve overlap is basically zero, but in practice there is a pump loss at low lift, so it should be a little positive. Since it becomes EGR cooled a little at the exhaust port, the knocking prevention effect can also be expected.

  G / F (25 or more) that does not generate NOx can be maintained up to a relatively high load even in a state where there is no supercharging. However, the total amount of fresh air and EGR can be increased by supercharging. G / F (25 or more) without generating NOx can be maintained until HCCI operation with very little NOx is possible. The use of a variable capacity risholm compressor enables highly efficient supercharging even at low pressure supercharging. Further, in the low load region, the mechanical supercharger stops driving by idling or a clutch to be in a natural intake state, and performs the above valve timing control.

[Natural intake HCCI (or SI) mode with low load (see operation areas g and h in FIG. 3, see FIG. 5 (c))]
(i) The mechanical supercharger stops its operation by idling or clutch, and the intake valve opening timing is separated from the top dead center so as to open slowly, and the mixture temperature is raised by the pump loss.

(ii) Further, as shown in FIG. 4C, a relatively small amount of EGR is introduced by setting the exhaust valve closing timing to, for example, 30 ° after top dead center. Further, the intake valve opening timing is set to 60 ° after the top dead center, for example, to reduce the intake air amount and increase the pump loss.

(iii) The intake valve closing timing is near the bottom dead center. When the G / F becomes too lean or in the SI mode, the intake valve closing timing is moved away from the bottom dead center in order to reduce the air amount.

  As the load decreases, the intake valve opening timing is delayed (minus OL) so that the ignition timing is not delayed. If the ignition timing is too early, adjust the exhaust valve closing timing earlier. If the intake valve opening timing is delayed, pump loss increases, and if the exhaust valve closing timing is delayed, the cycle efficiency decreases, so the optimal combination is set on the map and ignition is performed using the intake valve opening timing and exhaust valve closing timing. F / B control the timing.

  If G / F becomes too lean, the intake valve closing timing is advanced (or delayed) to reduce the amount of fresh air.

  In the fuel injection supply, the ignition timing can be controlled for each cycle by changing the ratio of the amount of fuel injected during the exhaust backflow and the amount of fuel injected during intake. For example, when the injection amount into the exhaust backflow is increased, the ignition timing is advanced. On the other hand, although NOx increases, it is also possible to stratify by injecting fuel during the compression stroke and to advance the ignition timing.

  In a low load region where the fuel is low and the A / F is lean, it is necessary to increase the temperature by EGR in order to keep the ignition at an appropriate position. However, if this is done, the G / F becomes too lean and the region where combustion does not occur increases and HC increases. Therefore, the fresh air amount is decreased by reducing the EGR amount by advancing the exhaust valve closing timing and delaying the intake valve opening timing to decrease the intake valve opening degree. By delaying the opening timing of the intake valve and setting it to minus overlap, it is possible to create a negative pressure in the cylinder, increase the pump loss and raise the gas temperature, and keep the ignition timing without delay.

  Moreover, the fresh air can be effectively reduced by separating the intake valve closing timing from the position after the bottom dead center. If the G / F is reduced, spark ignition is possible with a G / F of 20 to 25, and it is possible to connect to an unloaded or idle SI mode.

1 is a basic configuration diagram of an engine operation control apparatus according to an embodiment of the present invention. It is a system block diagram of the said engine operation control apparatus. It is a conceptual diagram which shows the operation area | region of the said operation control apparatus of an engine. It is a schematic diagram which shows the overlap of the said operation control apparatus of an engine, and a valve opening / closing timing. It is a conceptual diagram which shows the operation area | region of the said operation control apparatus of an engine. It is an overlap selection map in the said operation control.

Explanation of symbols

1 Engine 4 Valve system a to i Operating region OL Valve overlap BDC Bottom dead center TDC Top dead center IVC Intake valve closing timing IVO Intake valve opening timing EVC Exhaust valve closing timing

Claims (4)

A valve system capable of variably controlling at least intake valve opening timing (IVO), intake valve closing timing (IVC), and exhaust valve closing timing (EVC) is provided, and combustion of the engine is started by spark ignition according to the operation region. In an engine operation control device that operates in SI mode or HCCI mode in which combustion starts by premixed compression self-ignition,
In the high load SI mode, the valve overlap (OL) is controlled to be large and the center thereof is positioned near the top dead center (TDC), and the intake valve closing timing is set after the bottom dead center (BDC) or before An engine operation control device characterized by controlling to a separated position. A valve system capable of variably controlling at least intake valve opening timing (IVO), intake valve closing timing (IVC), and exhaust valve closing timing (EVC) is provided, and combustion of the engine is started by spark ignition according to the operation region. In an engine operation control device that operates in SI mode or HCCI mode in which combustion starts by premixed compression self-ignition,
In the medium load HCCI mode, the valve overlap is controlled to be small and the center thereof is located away from the top dead center, and the intake valve closing timing is controlled to be located near the bottom dead center. An engine operation control device. It has at least an intake valve opening timing (IVO), an intake valve closing timing (IVC), and a valve system that can variably control the exhaust valve closing timing (EVC), and the engine starts combustion by spark ignition according to the operating region. In an operation control device for an engine that operates in the SI mode or the HCCI mode in which combustion starts by premixed compression self-ignition,
In the low-load HCCI mode or the low-load SI mode, the valve overlap is controlled to be negative and the center thereof is located away from the top dead center, and the intake valve closing timing is located in the vicinity after the bottom dead center. An engine operation control apparatus characterized by controlling the engine. A valve system capable of variably controlling at least intake valve opening timing (IVO), intake valve closing timing (IVC), and exhaust valve closing timing (EVC) is provided, and combustion of the engine is started by spark ignition according to the operation region. In an engine operation control device that operates in SI mode or HCCI mode in which combustion starts by premixed compression self-ignition,
In the high load SI mode, the valve overlap (OL) is controlled to be large and the center thereof is positioned near the top dead center (TDC), and the intake valve closing timing is set after the bottom dead center (BDC) or before In the middle load HCCI mode, the valve overlap is controlled to be small and the center of the valve overlaps after the top dead center, and the intake valve closing timing is located near the bottom dead center. In the low load HCCI mode or low load SI mode, the valve overlap is controlled to be negative and the center of the valve overlaps after the top dead center, and the intake valve closing timing is near the bottom dead center. An operation control device for an engine, characterized by being controlled to be located at

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